The lift and drag properties of a wing are determined in wind tunnel tests. This is done by measuring the pressure upon the wing surface at various points along the wing. In order to alter the wing shape to improve the lift thereof it is helpful to know the location of the transition between the laminar and turbulent flow areas of the wing. This is so because in general laminar flow over the wing results in lift whereas turbulent flow results in drag. Thus, it is desirable to encourage laminar flow and discourage turbulent flow over most of the wing surface.
A method of measuring the pressure on the wing involves placing orifices at various points on the wing from the leading to the trailing edges. Pressure transducers are connected to the orifices via pneumatic tubes. The present method of detecting the transition between the laminar and turbulent flow areas requires an individual to enter the tunnel and listen to the noise at each of the orifices using a stethoscope. Since the noise level of laminar flow regions is relatively low compared to that of turbulent flow regions the transition between the two areas can be found rather accurately. However, there are several limitations imposed by this method. Firstly, an operator must be physically in the tunnel to connect his stethoscope to the orifices along the wing surface. Therefore, measurements cannot be made if the environment in the tunnel is hostile (e.g., the pressure is above or below atmospheric pressure) or if the space within the tunnel is limited. Secondly, the pressure measurements cannot be taken while the operator is listening to the noise since the stethoscope (essentially an open tube) introduces a leak into the system. Thirdly, the noise levels cannot be recorded and correlated.
It is therefore an object of the present invention to provide a system for detecting the transition between laminar and turbulent flow areas on a test surface that does not require an operator to enter the wind tunnel.
Another object of the present invention is to provide a system for detecting the transition between laminar and turbulent flow areas on a test surface that provides an electrical output to permit data input to a multitude of systems, such as a computer for data reduction and storage.
An additional object of the present invention is to provide a system for detecting the transition between laminar and turbulent flow areas on a test surface that allows pressure measurements to be taken simultaneously with noise level measurements.
The foregoing and other objects of the invention and many of the advantages attendant therewith will become apparent when the claims and description contained herein are considered in conjunction with the accompanying drawings.